In the Linux kernel, the following vulnerability has been resolved:
mm: blk-cgroup: fix use-after-free in cgwb_release_workfn()
cgwb_release_workfn() calls css_put(wb->blkcg_css) and then later accesses
wb->blkcg_css again via blkcg_unpin_online(). If css_put() drops the last
reference, the blkcg can be freed asynchronously (css_free_rwork_fn ->
blkcg_css_free -> kfree) before blkcg_unpin_online() dereferences the
pointer to access blkcg->online_pin, resulting in a use-after-free:
BUG: KASAN: slab-use-after-free in blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)
Write of size 4 at addr ff11000117aa6160 by task kworker/71:1/531
Workqueue: cgwb_release cgwb_release_workfn
Call Trace:
<TASK>
blkcg_unpin_online (./include/linux/instrumented.h:112 ./include/linux/atomic/atomic-instrumented.h:400 ./include/linux/refcount.h:389 ./include/linux/refcount.h:432 ./include/linux/refcount.h:450 block/blk-cgroup.c:1367)
cgwb_release_workfn (mm/backing-dev.c:629)
process_scheduled_works (kernel/workqueue.c:3278 kernel/workqueue.c:3385)
Freed by task 1016:
kfree (./include/linux/kasan.h:235 mm/slub.c:2689 mm/slub.c:6246 mm/slub.c:6561)
css_free_rwork_fn (kernel/cgroup/cgroup.c:5542)
process_scheduled_works (kernel/workqueue.c:3302 kernel/workqueue.c:3385)
** Stack based on commit 66672af7a095 ("Add linux-next specific files
for 20260410")
I am seeing this crash sporadically in Meta fleet across multiple kernel
versions. A full reproducer is available at:
https://github.com/leitao/debug/blob/main/reproducers/repro_blkcg_uaf.sh
(The race window is narrow. To make it easily reproducible, inject a
msleep(100) between css_put() and blkcg_unpin_online() in
cgwb_release_workfn(). With that delay and a KASAN-enabled kernel, the
reproducer triggers the splat reliably in less than a second.)
Fix this by moving blkcg_unpin_online() before css_put(), so the
cgwb's CSS reference keeps the blkcg alive while blkcg_unpin_online()
accesses it.
References
Configurations
Configuration 1 (hide)
|
History
28 Apr 2026, 20:45
| Type | Values Removed | Values Added |
|---|---|---|
| References | () https://git.kernel.org/stable/c/115a5266749dcde7fe4127e8623d19c752088f69 - Patch | |
| References | () https://git.kernel.org/stable/c/50879a3c1faf06e661090015d59e2127255cff27 - Patch | |
| References | () https://git.kernel.org/stable/c/67cb119d32f35e32acd0393bbeb318b2bb1fdafe - Patch | |
| References | () https://git.kernel.org/stable/c/8f5857be99f1ed1fa80991c72449541f634626ee - Patch | |
| References | () https://git.kernel.org/stable/c/dfc8292a1d6782c76b626315605e0585a5a18447 - Patch | |
| References | () https://git.kernel.org/stable/c/ea3af09eb87d8f8708c66747fcf1a2762902e839 - Patch | |
| CWE | CWE-416 | |
| CPE | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| First Time |
Linux
Linux linux Kernel |
27 Apr 2026, 15:16
| Type | Values Removed | Values Added |
|---|---|---|
| CVSS |
v2 : v3 : |
v2 : unknown
v3 : 7.8 |
27 Apr 2026, 14:16
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
27 Apr 2026, 12:16
| Type | Values Removed | Values Added |
|---|---|---|
| References |
|
24 Apr 2026, 15:16
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-04-24 15:16
Updated : 2026-04-28 20:45
NVD link : CVE-2026-31586
Mitre link : CVE-2026-31586
CVE.ORG link : CVE-2026-31586
JSON object : View
Products Affected
linux
- linux_kernel
CWE
CWE-416
Use After Free